A pallet is a flat transport structure made of either wood, plastic, paper, metal and composite material that can support a variety of goods in a stable fashion while being lifted by any mobile pallet lifting device. The purpose of the pallet is to improve storage and product distribution efficiency and to protect the product. Pallet serves equally as the interface between the packaged product and the roughness of the product distribution environment which includes many different vibrations and shocks during truck, rail or air transportation.
Today, it is estimated that there are more than one billion new pallets that are produced yearly worldwide. It is estimated that more than 93% of the pallets produced are made of wood. Due to the use of wood as a source, the consumption of wood for making wood pallets is now recognized as part of the deforestation which is a major contributory factor to global warming. The compressed wood pallet that uses Melamine Urea Formaldehyde (MUF) or Urea Formaldehyde (UF) as the binder may cause health hazards according to the International Agency for Research of Cancer. Other than the afore-mentioned environmental problems, wood pallets also carry risk of introduction and/or spread of quarantine pests. New guidelines named as “International Standards for Regulating Wood Packaging Material in International Trade” (ISPM 15) are set out to govern the use of wood packaging materials. Under the ISPM 15 guidelines, all wood pallets need to be either heat treated or fumigated so as to ensure that no living pests are being transported from one country to another. Unfortunately, not all types of wood can be heat treated and chemicals, especially methyl bromide, used for fumigation appears to cause health hazards.
Due to the afore-mentioned disadvantages of using wood packaging materials, alternative materials such as plastics, metal, composite materials have been used. However, these packaging materials are neither environmental friendly nor cost-effective. For example, the plastic pallet takes more than 100 years to be degraded. Plastic and metal pallets are also relatively more costly and heavier. As oil prices reach the new highs, it is no longer cost-effective to use plastic and metal pallets, especially for one-way transportation of goods by air as charges are more likely directed to the weight of packed cargo, including the weight of pallet.
Conventional open-molding process is mainly used for manufacturing of flat sheet or board. As there is no built-up wall along the parameter, the molded product usually requires trimming and has relatively low density. Composite materials used in such process only require the addition of low content binder without the use of filler material or flow promoter. However, the main disadvantages of open-molded product are that the profile of the molded product is limited to the flat sheet and usually with a standard size. The wastages from trimming the four edges are also relatively high. It is not cost-effective in terms of material utilization.
Comparing with open-molding process, products produced by typical close-molding process have relatively higher density and can result in a more complex profile of the molded product. There is also no material wastage as no trimming of edges is required. However, most of the conventional close-molded products still relies on the use of metals and plastics which are more costly and environmental unfriendly. Alternative methods as described in patent publications WO2005/120787 and WO/2005/120967 have used wood fibers as a basic material to form moldable mixture. These references use relatively high percentage of wood fibers and use high percentage of Melamine Urea Formaldehyde as a liquid binder in their moldable mixture for molding their product. The liquid binder used in their moldable mixture carries formaldehyde to the molded product which is known to be harmful to the environment and probably harmful to our health. As a result, expensive exhaust systems are required to eliminate the formaldehyde during processing under a controlled environment.
The moldable mixture used in WO 2005/120787 and WO 2005/120967 also require the use of soya extract as a de-molding agent for ease of removing the molded product from the mold, and the use of palm fibers as an impact modifier for providing a cushioning effect for the molded product. The moisture content of the moldable mixture according to these methods is also relatively high because liquid binder is used. The products molded with wood fiber usually have lower impact and bending strength because wood fibers are relatively brittle and difficult to flow. In order to produce product with the desired properties such as high impact and bending strength, high density, and more importantly the desired profile, additional additives are used by these approaches to form the moldable mixture, and significant amount of liquid is also needed to facilitate the flow of the moldable mixture in the mold so as to form the desired profile and strength.
The disadvantages of using large amount of liquid binder to facilitate the flow of the moldable mixture in the molding process include: a) the high content of moisture vaporized during the molding process increases the pressure in the molding mixture which in turn increases the risk of the molded product being delaminated when the mold is opened because of the sudden release of pressure; b) the high water content in the liquid binder may dilute the added adhesive to certain extend resulting in longer molding time and therefore hardener which is for the acceleration of the hardening process is needed to ensure that the molded product is fully cured in the mold before it can be ejected out; c) the high pressure generated through the moisture/liquid vaporizing process may cause mold explosion if the pressure is not released in time. Pressure vents are therefore incorporated in the mold design which is tedious and expensive; and d) the molded product produced with such process is usually prompt to fungus attack, and has relatively high shrinkage and they warp easily due to high moisture content in the molded product; e) an additional ironing process by opening and closing the mold repeatedly to allow the excess moisture/steam to escape during molding process is needed so as to give sufficient time for the molded product to cure in the mold before ejecting it out.
In addition, the methods disclosed in Patent Publications WO 2005/120787 and WO 2005/120967 use ammonium chloride as a hardener to harden the molded product in the mold before it is ejected out because the moldable mixture had high moisture content. Hardening agent is easily hardened in high temperature and as such high temperature has to be avoided in the conventional molding process. On top of this, soya extract is also used as the de-molding agent to facilitate the ejection process. The main disadvantage of using soya extract is that the soya extract may not facilitate the bonding among wood cells of the wood fibers. More liquid binder is therefore needed to provide a desirable bonding property. However, the more the binder is used, the more the formaldehyde is emitted during the molding process.
Another alternative way to achieve a desirable molded product is to use a moldable mixture with low moisture content. However, it is difficult to mold a product with a complex profile if the moldable mixture contains a material which is difficult to flow in the molding cavity with low moisture content. In addition, the lower is the moisture content, the lower is the drawing ratio. The drawing ratio is an index of how the moldable mixture can be flown in an enclosed mold.
In view of the afore-mentioned problems associated with the use of wood pallets, be it environmentally, health or cost, and all other alternate pallets available in the market, in one way or another has its own shortcomings. It is therefore primarily important to come out with a new moldable mixture which is free of formaldehyde and low in moisture content. Methods of manufacturing molded products and related parts which are cost-effective, safe and capable of producing high density, light weight and more complex molded products are also important.